The cabin of a modern passenger aircraft is air-conditioned usually both when the aircraft is flying and is on the ground by means of the aircraft's own air conditioning system. The aircraft air conditioning system is supplied with bleed air which is taken from the engine compressors or auxiliary power unit compressors and cooled to a desired low temperature in the air conditioning units, the so-called air conditioning packs of the aircraft air conditioning system. The air cooled in the air conditioning packs of the aircraft air conditioning system is led into a mixer where it is mixed with recirculation air sucked from the aircraft cabin. The mixed air produced in the mixer and composed of cold fresh air provided by the air conditioning packs and of recirculation air sucked from the aircraft cabin is finally led into the aircraft cabin for air-conditioning of the aircraft cabin
In wide-body aircraft, in particular in wide-body aircraft having two passenger decks extending over the entire length of the aircraft, an air conditioning system described, for example, in DE 44 25 871 C1 and comprising two recirculation systems for sucking exhaust air from the aircraft cabin is used at present. A low-pressure recirculation system extracts air from an upper deck region of the cabin, while a high-pressure recirculation system serves to extract air from a middle deck region of the cabin. The recirculation air removed from the middle deck region of the cabin by the high-pressure recirculation system is blown into a central mixer of the aircraft air conditioning system. In contrast, the air sucked from the upper deck region by the low-pressure recirculation system is supplied to local mixers which are fed with premixed air by the central mixer, i.e. an air mixture composed of cold fresh air provided by the air conditioning packs and recirculation air from the middle deck region of the cabin. The air mixture, produced in the local mixers, composed of premixed air from the central mixer and recirculation air from the upper deck region of the cabin is finally used for air-conditioning the aircraft cabin. In particular, air is led into the middle deck region of the cabin from a local mixer arranged in the region of the middle deck, while air is blown into the upper deck region of the cabin from a local mixer arranged in the region of the upper deck.
An air conditioning system equipped with two recirculation systems is designed so that both recirculation systems must always provide a defined minimum air flow in order to ensure sufficient ventilation of the aircraft cabin. In the operation of the aircraft air conditioning system, therefore, it is not possible to switch off one recirculation system or both recirculation systems. In the operation of the recirculation systems, however, the waste heat produced by the fans of the recirculation systems gives rise to additional heat loads. The cooling energy required for cooling the recirculation fans has to be provided by the air conditioning system, so that the operation of the recirculation systems reduces the cooling capacity available for the cooling of the aircraft cabin.
In particular when the aircraft is on the ground on hot days, the additional heat input of the recirculation systems can significantly increase the time required for cooling the aircraft cabin to a desired temperature. The air conditioning system then requires a longer run-up period until the cabin is sufficiently cooled and passenger boarding can start. As a result, the turnaround of the aircraft at the airport is slowed down. Since the air conditioning system is supplied with bleed air from the auxiliary power unit compressors in this operating phase, the increased run-up period of the air conditioning system also gives rise to increased fuel costs. Finally, the operating time of the auxiliary power unit is increased, which may lead to higher maintenance costs.
The invention is directed at the object of specifying a system and a method for air-conditioning an aircraft cabin which allow a shortening of the time required for cooling the aircraft cabin when the aircraft is on the ground.